This invention relates to television synchronization apparatus and especially to apparatus for providing field conversions during the synchronizing of television signals from two or more non-synchronous sources of video information.
In modern television programming, it is generally necessary to integrate a mix of external and studio video sources smoothly into live programs. An example of such a requirement is the increasing use of Electronic Journalism (EJ) facilities for on-the-spot news broadcasts. The wide diversification of such program sources has emphasized the need for synchronizing systems to incorporate non-synchronous video signals originating outside the local studio. Integrating a non-synchronous source into an existing program presents a serious production problem, since it is necessary to gen-lock studio sync to the outside signal or to use additional sync generators for the proper timing reference. Gen-locking to the external non-synchronous source is particularly troublesome in that only one source at a time may be utilized and that source tends to disrupt the internal studio sync timing. The use of multiple sync generators is expensive and creates further operational difficulties in maintaining gen-lock between the multiple generators. Similar problems are encountered in network cable and satellite transmission systems even though expensive rubidium standards are used because changes in the electrical path length causes the color phase of the video signal to drift, even though the horizontal signal timing component may be relatively stable.
A video synchronizer may be advantageously used to overcome the problems of incorporating non-synchronous program sources into a local studio broadcast where the conventional gen-locking methods described above do not provide a satisfactory solution. A video synchronizer is primarily a digital device, which accepts a non-synchronous video signal input from any external source, converts the signal from analog to digital format; stores the digitized signal in a memory; converts the digital signal back to analog form and processes the reconverted signal through a signal processing amplifier wherein sync, blanking and color burst signals are added to the output video signal. The digitized video information stored in memory is read out of the memory at a rate which is synchronous with the local studio sync generator timing. Since the reconstituted video signal is now completely synchronous with the local studio reference, it may be used directly for mixing, special effects, etc., similar to the manner in which a live camera, a video tape machine or other studio source is used.
However, in a synchronizer that does not individually store each of the four unique color fields of the NTSC system, provisions must be made for converting the video of each of these four unique fields into some other fields because of the unknown and random timing relationship between the non-synchronous input and the known timing of the house reference. For example, in a synchronizer which employs only one field of storage, it must be possible to modify any of the four input fields to be used as any of the four output fields. In a frame synchronizer, it must be possible to modify either of the two input odd fields or even fields to be used as any of the two output odd fields or even fields, respectively. cl SUMMARY OF THE INVENTION
A television signal synchronizer apparatus is providing for making field conversions between an input video signal and an output video signal, the input and output video signals being non-synchronous.
The apparatus comprises input and output video processing means adapted to be coupled to memory storage means.
A source of independent reference signals having a non-variant field sequence.
Memory control means including memory input means for writing the input video signal into the memory storage means and memory output means for reading the output video signal out of the memory storage means.
Means for developing field identification signals from one of the input video signal or the independent reference signal.
Means for developing a source of field conversion signals from the field identification signals and the nonvariant field sequence signal.
Delay means coupled to the memory input and the memory output means responsive to the source of field conversion signals and the field identification signals for modifying the writing and reading of data in and out of the memory storage means so as to provide field conversions consistent with the non-variant field readout sequence.